The invention relates to a machine having a rotor which is mounted such that it can rotate about a rotation axis and has a rotor external housing which is attached to rotor shaft parts and surrounds a winding former with a winding that is to be cooled, in particular a superconductive winding. The rotor also has a device to hold the winding former within the rotor external housing, which device comprises, at least at one end of the winding former, a device which transmits torque between the winding former and the associated rotor shaft part with at least one rotationally symmetrical composite body composed of a plastic reinforced with fiber material. A corresponding machine is disclosed in U.S. Pat. No. 5,880,547 A.
Special types of electrical machines, in particular generators or motors, have a rotating field winding and a stationary stator winding. In this case, the current density and thus the specific power of the machine, that is to say the power per kilogram of its own weight; can be increased, and the efficiency of the machine can also be increased, by the use of cryogenically cooled and in particular superconductive conductors.
Cryogenically cooled windings of electrical machines generally have to be thermally isolated from the environment and have to be kept at the required low temperature by a coolant. Effective thermal isolation can in this case be achieved only by the cryogenically cooled parts of the machine being separated as far as possible from the warm external area by a vacuum with a residual gas pressure of generally less than 10−3 mbar, and by the connecting parts between these cryogenically cooled parts and the warm external area transmitting as little heat as possible. Two variants, in particular, are known for vacuum isolation of rotors with rotor windings which have to be cryogenically cooled and with warm stator windings:
In a first embodiment, the rotor has a warm external housing and an encapsulated vacuum area which rotates with the rotor. The vacuum area should in this case surround the cryogenically cooled area on all sides (see, for example, “Siemens Forsch. u. Entwickl.-Ber. [Siemens Research and Development Reports]”, Vol. 5, 1976, No. 1, pages 10 to 16). However, heat is transferred undesirably to the cryogenically cooled parts via the supports which extend through the vacuum area.
In a second embodiment, the essentially cold rotor rotates in a hard vacuum. In this case, the outer boundary of the hard vacuum area is defined by the internal bore of the stator. However, an arrangement such as this requires shaft seals which can resist a hard vacuum between the rotor and the stator (see, for example, DE 27 53 461 A).
The first-mentioned variant is provided in the machine which can be found in the cited US-A specification. Accordingly, a superconductive winding for its rotor is located in the interior of a rotor cryostat which, together with flanged shafts that are fitted, forms an external housing for the rotor. Helium cooling is provided for the winding superconductors. In contrast, the external contour of the rotor external housing is approximately at room temperature, or even above room temperature during operation. The useful torque from the machine is produced in the rotor winding. This rotor winding is arranged in a cold winding former which is itself suspended and held in an isolated form in the rotor external housing, which acts as a cryostat. In this case, this suspension or retention on the drive end of the rotor, which is frequently also referred to as the A side of the machine, must be sufficiently robust to transmit the torque from the cold winding former to a warmer shaft part on the drive end. A corresponding, rigid connecting device for torque transmission therefore has to be designed to be relatively massive and must be connected to the winding former and to the shaft part on the drive end such that power can be transmitted. This means that heat is unavoidably introduced into the cold area of the rotor. It is therefore frequently necessary to cool the connecting device which transmits the torque (see, for example, “Handbook of Applied Superconductivity”, Vol. 2: Ed.: B. Seeber, Institute of Physics Publishing, Bristol (GB), 1998, pages 1497 to 1499 and 1522 to 1530). At the same time, this connecting device also provides the drive-side centering for the cold winding former. Virtually no torque is emitted on the opposite rotor side, which is also referred to as the non-drive end or in general as the B side, where important connections, such as a coolant supply, are provided for operation of the machine. Only the functions of centering and thermal isolation therefore, essentially, have to be carried out here. Furthermore, measures to compensate for shrinkage of the cooled winding former are planned there.
In order to reduce the amount of heat which is introduced into the cooled superconductive area of the rotor, one specific embodiment of the machine that is disclosed in the cited US-A specification provides for the connecting device which transmits the torque to have, at least on the drive end, a hollow-cylindrical composite body composed of a glass-fiber-reinforced plastic. This hollow cylinder is provided at each of its two axle ends with a steel attachment part, which is connected to the winding former and to the drive shaft such that power can be transmitted. The mechanical connection between the plastic hollow cylinder and the steel attachment parts has to ensure good resistance to overloads and a long fatigue life when subjected to alternating loads, since, for example during starting and in various fault situations on motors such as these, considerably higher torques than those during normal operation occur and must not lead to damage to the device which transmits the torque. However, the US-A specification does not contain any details relating to this.
Such details are addressed in U.S. Pat. No. 6,129,477 A. In this case, a conically running surface is used to transmit torque between the various parts of this device, which are composed of materials with different shearing moduli via a connecting device, with the intention of bonding occurring between these parts on this surface. A first part of the connecting device is in this case composed of a glass-fiber-reinforced plastic, while a second part is made of metal. In this case as well, the functionality of the torque transmission depends to a major extent on the fatigue life of the bond between these parts.
In addition to metallic superconductor materials such as NbTi or Nb3Sn which have been known for a long time and as are used in the machines mentioned above, metal-oxide superconductor materials with critical temperatures above 77 K have also been known since 1987. Attempts have been made to use conductors based on such high-Tc superconductor materials, which are also referred to as HTC materials, to produce superconductive windings for machines (see, for example, WO 98/02953 A). Owing to the temperature differences between the operating temperature of the superconductor material and the external temperature on the warmer rotor external housing, even machines of this conductor type require measures to reduce the temperature that is introduced into the superconductive area.